This invention relates to a vertical plug-in single-in-line circuit module, and, more particularly, this invention relates to an improvement to a vertical plug-in circuit module for dissipating heat from an electrical component on the circuit module.
Vertical plug-in circuit modules are known in the art, and it is also known that there are various problems associated with these circuit modules. An important problem associated with these circuit modules is the dissipation of heat energy from the components located on these circuit modules.
Normally a circuit module includes a carrier composed of a ceramic. Components such as film resistors are located upon the carrier. When electrical power is supplied to the resistors the carrier is locally heated most intensely adjacent to the resistors. Depending on the heat conductivity of the carrier, the heat is conducted away from the resistor at a certain rate. This heat can be dissipated from the carrier and the resistor via cooling air. However, since the thermal conductivity of the carrier and the heat dissipating ability of the cooling air are limited, the resistor and adjacent area of the carrier can experience very high local temperatures under conditions when heat can not be dissipated at a sufficient rate. These conditions can include obstruction of air flow, increases in power supplied to the resistor and high ambient air temperatures. This intense local heating of the carrier can induce unsatisfactory temperature gradients in the carrier which results in thermal stresses in the carrier which can crack the carrier. Also, the heating and cooling cycles to which the carrier is exposed can cause thermal fatigue of the carrier.
One way of dealing with the heat dissipation problem is to add a plate having good heat conduction characteristics, to one side of the carrier. Metalic plates such as an aluminum plate have been used for this purpose. Aluminum has a heat conductivity over ten times better than many ceramic carriers, therefore it is a desirable material. Favorable heat dissipation is achieved using plates, and this results in lower temperature gradients along the carrier.
In light of the foregoing, it can be appreciated that heat dissipation from a plug-in circuit module is a problem and that the use of a metal plate may not be a satisfactory solution where cost and size considerations are important.